Preservation of many liquids such as juices or other liquid foods or medicines requires killing of microbes, such as bacteria, viruses and spores, in the liquid. It may also be necessary to inactivate enzymes which can catalyze undesired reactions in the liquid. Pasteurization is the most commonly used process for the purpose. Pasteurization requires heating of the liquid to temperatures which can degrade the quality of the liquid. Heating of liquid foods for example can adversely affect the taste and nutritional quality of the food.
It has heretofore been recognized that liquids can be sterilized and preserved by contacting the liquids with pressurized dense CO.sub.2 (carbon dioxide). The process does not require heating of the liquids to damaging temperatures. Prior processes and equipment for this purpose have not been ideally suited for commercial operation.
Some prior processes are static in that the dense CO.sub.2 and liquid are simply allowed to stand together in a pressure vessel for a period of time. The production rate of treated liquid is undesirably low. Other prior processes are dynamic in that a forced dispersion of a flow of dense CO.sub.2 into a flow of the liquid is brought about in a column which contains conventional packing such as rashig rings or a frit. Dispersive processes of this kind increase the production rate of treated liquid by creating a greater interfacial contact area between the dense CO.sub.2 and liquid than is present in the static processes. A still greater interface area between the liquid and dense CO.sub.2, in a given volume of flow, would be advantageous.
Dispersive processes of the above discussed kind are also subject to other problems. For example, emulsification of the liquid and dense CO.sub.2 can occur necessitating further steps to break the emulsion. Processing of liquids of certain densities may not be practical as a density difference between the liquid and dense CO.sub.2 is needed in order to separate the two. Fouling of components within the processing vessel may occur if the liquid contains suspended particulate matter.
The present invention is directed to overcoming one or more of the problems discussed above.